January 24, 2004
Donald Savage
Headquarters, Washington
(Phone: 202/358-1547)
Guy Webster
Jet Propulsion Laboratory, Pasadena, Calif.
(Phone: 818/354-5011)
RELEASE: 04-036
SPIRIT CONDITION UPGRADED AS TWIN ROVER NEARS MARS
Hours before NASA's Opportunity rover reaches Mars, engineers have
found a way to communicate reliably with its twin, Spirit.
Engineers are working to get Spirit's computer out of a cycle of
rebooting many times a day.
Spirit's responses to commands sent Saturday morning confirmed a
theory the problem is related to the rover's two "flash" memories or
software controlling those memories.
"The rover has been upgraded from critical to serious," said Mars
Exploration Rover Project Manager Peter Theisinger at NASA's Jet
Propulsion Laboratory, Pasadena, Calif. He predicted significant work
is still ahead for restoring Spirit.
Opportunity is on course for landing in the Meridiani Planum region of
Mars. That point was selected months ago. Mission managers chose not
to use an option for making a final adjustment to the flight path.
"We managed to target Opportunity to the desired atmospheric entry
point, which will bring us to the target landing site, in only three
maneuvers," said JPL's Dr. Louis D'Amario, navigation team chief for
the rovers.
Opportunity will reach Mars at 12:05 a.m. Sunday EST. From the time
Opportunity hits the top of Mars' atmosphere at about 5.4 kilometers
per second (12,000 miles per hour) to the time it hits the surface
six minutes later, then bounces, the rover will be going through the
riskiest part of its mission. Based on analysis of Spirit's descent
and on weather reports about the atmosphere above Meridiani Planum,
mission controllers have decided to program Opportunity to open its
parachute slightly earlier than Spirit did.
Mars is more than 10 percent farther from Earth than it was when
Spirit landed. That means radio signals from Opportunity, during its
descent and after rolling to a stop, have a lower chance of being
detected on Earth. About four hours after the landing, news from the
spacecraft may arrive by relay from NASA's Mars Odyssey orbiter.
However, that will depend on Opportunity finishing critical
activities, such as opening the lander petals and unfolding the
rover's solar panels, before Odyssey flies overhead.
Spirit has 256 megabytes of flash memory, a type commonly used on gear
such as digital cameras for holding data even when the power is off.
Engineers confirmed Spirit's recent symptoms are related to the flash
memory, when they commanded the rover to boot up and use
random-access memory instead of flash memory. The rover obeyed
commands about communicating and going into sleep mode. Spirit
communicated successfully at 120 bits per second for nearly an hour.
"We have a vehicle that is stable in power and thermal, and we have a
working hypothesis we have confirmed," Theisinger said. By commanding
Spirit into a mode that avoids using flash memory, engineers plan to
get it to communicate at a higher data rate, diagnose the cause of
the problem and develop ways to restore as much function as possible.
The work on restoring Spirit is not expected to slow the steps in
getting Opportunity ready to roll off its lander platform. For
Spirit, those steps took 12 days. The rovers' main task is to explore
landing sites for evidence in the rocks and soil to determine if past
environments were watery and possibly suitable for sustaining life.
JPL, a division of the California Institute of Technology in Pasadena,
manages the Mars Exploration Rover project for NASA's Office of Space
Science, Washington. Images and additional information about the
project are available from JPL at:
http://marsrovers.jpl.nasa.gov
Information is also available from Cornell University, Ithaca, N.Y.,
at:
http://athena.cornell.edu
-end-